1. Field of the Invention
This invention relates to a universal connector and, more specifically, to a universal connector capable of temperature compensation.
2. Background and Brief Description of the Prior Art
Temperature compensating universal connectors have been known in the prior art and find use in many areas, such as, for example, in thermocouple and millivolt calibrators. In such thermocouple and millivolt calibrators, which are used to calibrate thermocouple input temperature indicating or transmitting instruments or which are to be connected to a thermocouple to measure and display the temperature of the thermocouple hot junction in degrees Fahrenheit or Celsius, the instrument is either the source for or the receiver of thermocouple based signals, the magnitudes of which are in the millivolt range. To be useful, the generated or received thermocouple based signals must be cold junction compensated before they can be interpreted into or out of temperature values.
The above noted instruments are capable of being connected to one of three different types of thermocouple wire sets or copper wires for the millivolt applications, one at a time. This is made possible by constructing the input/output connector of copper and sensing the temperature of the connector copper such that an appropriate compensation may be computed for the appropriate thermocouple half-junctions which exist when thermocouple wires are mated to the copper parts of the connector. Direct half-junction compensation has been used in the prior art.
Thermocouple wires come in different gages or diameters. Frequently, thermocouple wires are terminated in a variety of thermocouple material connectors. These connectors come with pins of various diameters, flat blades and different pin or blade spacings.
The problem of thermocouple compensation is well known in the art. Two criteria are of importance. First, the degree of compensation for the type of thermocouple wire in use over a range of steady ambient temperature typical of the use of the instrument and, second, compensation for dynamic temperature changes. The first criterion is of importance to all instruments. However, the second criterion is of particular importance in the case of portable instruments. Here it is necessary to expect that the instrument will be moved from hot to cold regions and vice-versa with availability for measuring or calibrating being expected by the user more or less on an immediate basis. The problem, as a practical matter, arises when the instrument is transported to a job site at a temperature substantially different from that encountered at the job site and is immediately placed into use on thermocouple wires or connectors which are of a quite different temperature. In making the transition from one to another temperature environment, the instrument, additionally, may be subject to an internal temperature gradient. Different parts of the same instrument, for external or internal reasons, may make the temperature transition at different rates. Similarly, the two metallic components of the connector or thermocouple wires will not necessarily be at the same temperature. These effects, combined in various scenarios, have produced errors in the past of several degrees Fahrenheit with a duration of many minutes. Until the transient effects are dissipated, an accurate measurement can not be made and the user is forced to linger for the duration of the transient.
In the prior art, Schmitz (U.S. Pat. No. 4,804,272) teaches a procedure for sensing the temperature of a termination by using a thermal bridge (block) between the critical position on the terminal block and the thermal sensor, the sensor being buried for effectiveness in the thermal bridge. There is no provision for permitting two different electrical circuits to benefit from the single sensor or to capture wires or connector pins of different sizes.
The patent to Muller (U.S. Pat. No. 2,410,098) emphasizes providing a gas tight connection through a bulkhead which can be disengaged from either side. The need for thermal compensation is avoided by making mating parts of matching alloys. Neither the issue of sensing the connection temperature nor the issue of capturing wires or pins of different sizes is raised.
The patent to Loiterman (U.S. Pat. No. 4,776,706) relates to a connector and compensating terminal apparatus for use with temperature responsive instruments to accommodate sensing devices such as thermocouples and resistance temperature devices (RTDs) having a wide plurality of lead connectors. The apparatus includes a temperature compensating block assembly having first and second conductive blocks coupled together at opposing surfaces by means of a thermally conductive and electrically insulative material, a corresponding surface of each block being adapted to receive one lead of a thermocouple sensor or RTD, which lead is held in contact on the surface of the block by a holding block having a corrugated holding surface and which holding block is movably mounted with respect to the conductive block to provide a variable spacing to enable the apparatus to accommodate the different types of thermocouple or RTD lead connectors. Additionally, there are two outside conducting blocks for two of the 3 or 4 RTD leads, which leads are also held in place by the respective holding blocks. This patent requires two holding block and two screws for operation thereof to accommodate the different wire or connector pin sizes and requires pushing of wires or pins into the blocks. The pushing requires that the instrument housing and circuit board must be structurally strong enough to tolerate the pushing action. Also, Loiterman maximizes the thermal mass of the copper blocks.